I. Field of the Invention
This invention relates to window film, more particularly to solar control film used for retrofit improvement of motor vehicle windows.
II. Description of the Prior Art
Window film for motor vehicle windows, which film was dyed in a vignette pattern to admit relatively little light above the sight line and was shaded down to clear film below the driver or passenger's sight line, was first introduced for use in original equipment laminated windshield glass and was the subject of U.S. Pat. Nos. issued to Ryan, 2,609,269; 2,636,420 and 2,639,687. The film was dipped in an appropriate dye for a controlled time to produce a gradient from dark to light, which will be referred to hereinafter as a vignette, and the film was sandwiched between panes of glass to make a safety windshield.
More recently, polymeric film useful for retrofit application to existing motor vehicle windows has been introduced to the automotive aftermarket.
Wildorf, for example, in U.S. Pat. Nos. 3,775,226 and 3,891,486 has a well rounded discussion of the prior art retrofit window film, and describes a typical prior solar control film comprising a polymeric sheet, a vapor deposited aluminum coat, a protective polymeric coat, and a pressure sensitive coat, which is deactivated initially by the presence of an agent that eliminates tack during storage, as well as during the time the film is being applied to the window, etc. Wildorf shows a laminated sequence of a moisture permeable polymeric stratum, a bonding stratum, a vapor deposited aluminum stratum, and a second moisture permeable polymeric stratum. All of these strata except the aluminum stratum are optically clear and transparent. The polymeric strata are made of a polyester such as polyethylene terephthalate. The vapor deposited aluminum stratum referred to is produced by controlled density, vapor vacuum deposition upon the surface of polymeric stratum, which produces a uniform thickness of metal. The polymeric strata range in thickness from 1/4 mil to 1 mil, preferably one-half mil. The vapor deposited aluminum has a thickness of no more than 300 angstrom units and is characterized by a light transmission of 5% to 60%. It goes on to explain a preferred adhesive in thickness from 0.1 to 0.3 mil.
Wildorf discloses, as a preferred transparent polymeric film--a polyester--for this laminate, a biaxially oriented polyethylene terephthalate. Other polymers which can be made into suitable film include polyvinyl fluoride, polyvinylidene fluoride, polycarbonates, polystyrene, polymethyl, methacrylate, polyamides, ionomers, etc. as well as esters and mixed esters of cellulose, and stabilizers against degradation caused by ultroviolet light may be included if desired. Film may also be made of a polymer of monomers consisting of essentially lower alkylene monomers; acrylonitrile, and polyethylene, polypropeylene and polyacrilonitrile.
Wildorf '486 also suggests that a colorant, preferably a dye, may be put in the adhesive stratum.
Wildorf's adhesive stratum is cast from a ketonic and/or alcoholic solution of the thermosetting polymer or acrylic. The solution preferably being applied to the clear film prior to superposing of the two polymeric films in the formation of the final product. For example, a polyester is Mylar, the acrylic is a methyl and/or ethyl methacrylate, the ketone is methylethyl and the alcohol is toluol.
Wildorf, U.S. Pat. No. 3,956,559 says his film has a pleasant soft grey color that permits excellent visibility (This is the natural color of aluminum on film, if looking through the film. Looking at the film, the impression is mirror-like). In other alternative embodiments Wildorf says that the polyester strata may be polyethylene terephthalate layers impregnated with fade resistant azo dyes.
Burger, U.S. Pat. No. 4,095,013 and Wildorf U.S. Pat. No. 3,949,134 show the use of a cling adhesive.
The conventional prior art method of depositing metal on polymeric film is vacuum deposition because it is faster, is dependable, and is inexpensive. A special kind of vacuum deposition of metal involves the sputtering method, which is substantially more expensive. For the purpose of this application vacuum deposition other than sputtering will be referred to as conventional vacuum deposition.
Applicant is not aware of any public use, knowledge, or writing prior to this invention that appreciates and teaches, for use on windows, the benefits of the steps of tinting polymeric film followed by high density vignette metallizing by conventional vacuum deposition of a second polymer foil, and laminating the two polymeric foils with the metal stratum positioned outwardly relative the auto interior and the dye layer, to produce a non-glare, high density, metallized composite.
In the retrofit automotive film industry, the conventional wisdom is that a composite film metallized by conventional vacuum deposition processes cannot be used on a vehicle because presenting the metallized surface to the outside would produce an unacceptable glare to persons outside the vehicle, and presenting the metallized surface to the inside of the vehicle would create hazardous glare or mirror effect to the occupant. In consideration of the glare factor, it was also thought necessary to put very low limits on the density of the metallic layer on the film. Consequently, the prior art constructions placed the metal to the inside facing the interior and at very low densities. In the prior art thinking and structures the degree of opacity to visible light transmission required to be effective in conventional vacuum metallizing of polymeric film would make the metal layers so highly reflective as to be unacceptable.
Since 1981 an additional constraint on allowable values of reflectivity have been imposed, and visible light reflectivity of greater than 35% has been banned by VESC 20. VESC is a voluntary association of state safety agencies and industry whose membership is dedicated to highway safety. Its members include all U.S. states and its standards usually become law in many states. Composite films cannot be made to conform to the reflectivity constraints with less than 45% transmission using conventional vacuum deposition techniques, although some success with sputtering exotic metals has been achieved. However, sputtering is a much more expensive method.
In the prior art, a light transmission on the order of 20-30%, for example, implies reflectivity of 70-80%.
Accordingly, it is a goal of this invention to create a composite film that has an area of very low light transmission, as low as 10% for example (a high density), and no greater than 35% reflectivity, by means of conventional vacuum deposition of metal. This invention is concerned with how that goal is met.